Schottky barrier semiconductor devices are widely used in many electronic applications ranging from high frequency or microwave frequency applications to high power applications. Schottky barrier semiconductor devices include, for example, Schottky diodes, High Electron Mobility Transistors (HEMTs), and Metal Semiconductor Field Effect Transistors (MESFETs). In each type of Schottky barrier semiconductor device, there is a Schottky gate contact that forms a Schottky barrier to an underlying semiconductor structure. A Schottky barrier is a potential barrier formed at a metal-semiconductor junction. The length of the Schottky gate contact (i.e., a gate length of the Schottky barrier semiconductor device) is a critical dimension of Schottky barrier semiconductor device. The length of the Schottky gate contact directly impacts a frequency response (i.e., the frequency of operation) of the Schottky barrier semiconductor device as well as other operational parameters of the Schottky barrier semiconductor device such as, for instance, transconductance.
It is particularly desirable for high frequency applications to minimize the length of the Schottky gate contact and thus the gate length of the Schottky barrier semiconductor device. Conventional processes for forming Schottky gate contacts consist of photoresist patterning followed by an etch of a dielectric down to the surface of an underlying semiconductor structure. The Schottky gate contact is then formed in the opening in the dielectric such that the length of the Schottky gate contact, and thus the gate length of the Schottky barrier semiconductor device, is defined by the length of the opening in the dielectric. However, an optical step size of a conventional optical stepper used for patterning the photoresist is limited to 0.4 micrometers. As a result, the minimum gate length achievable using conventional processing is 0.4 micrometers. Thus, there is a need for a Schottky gate contact that provides a reduced gate length and methods of fabrication thereof.